O'Neal Steven W, Hoover Angie M
Department of Biological Sciences, Southwestern Oklahoma State University, 100 Campus Drive, Weatherford, Oklahoma, 73096, USA.
Division of Coastal Sciences Study, Gulf Coast Research Laboratory, 703 East Beach Drive, Ocean Springs, Mississippi, 39564, USA.
J Phycol. 2018 Dec;54(6):818-828. doi: 10.1111/jpy.12786. Epub 2018 Oct 15.
Filaments in the surface layers of metaphytic mats are exposed to high photon flux densities of PAR and UVBR. We investigated the effect of UVBR exposure on growth of eight isolates of common metaphytic algae (Cladophora, Mougeotia, Oedogonium, Pithophora, Spirogyra, and Zygnema) acclimated to either high or low PAR levels prior to UVBR exposure. All isolates acclimated to low PAR exhibited significant reductions in growth rate caused by the UVBR exposure (P < 0.05). Acclimation to high PAR resulted in seven of the isolates being more tolerant of the UVB exposure. The two Zygnema isolates exhibited the most pronounced effect of high PAR acclimation with growth rates of UVB exposed treatments being equal to that of controls (P > 0.05). High PAR acclimation also protected chlorophyll a levels in the Zygnema isolates. Absorption of UVB by methanol extracts increased 322%-381% for the two Zygnema isolates when high PAR acclimated. The broad absorption peak at 270 nm suggests that phenolic compounds were responsible. Previous studies have shown that Zygnema isolates from extreme environments tolerate UVBR and contain UVB screening compounds, but our results extend these adaptions to Zygnema from typical temperate zone habitats. Although none of the other metaphytic algae produced UVB absorbing compounds, they all exhibited higher growth rates under UVBR exposure following high PAR acclimation. This suggests that the algae evaluated have inducible defenses against UVBR exposure that coupled with their mat structure would provide an adaption to the challenging light environment in shallow-water habitats.
附生植物垫表层的丝状藻类会受到高光量子通量密度的光合有效辐射（PAR）和紫外线B辐射（UVBR）的影响。我们研究了UVBR照射对8种常见附生藻类（刚毛藻属、转板藻属、鞘藻属、团藻属、水绵属和双星藻属）生长的影响，这些藻类在UVBR照射前已适应高或低PAR水平。所有适应低PAR的分离株在UVBR照射后生长速率均显著降低（P < 0.05）。适应高PAR使其中7种分离株对UVB照射更具耐受性。两种双星藻属分离株表现出高PAR适应的最显著效果，UVB照射处理的生长速率与对照相等（P > 0.05）。高PAR适应还保护了双星藻属分离株中的叶绿素a水平。对于两种适应高PAR的双星藻属分离株，甲醇提取物对UVB的吸收增加了322% - 381%。270 nm处的宽吸收峰表明是酚类化合物起了作用。先前的研究表明，来自极端环境的双星藻属分离株耐受UVBR并含有UVB筛选化合物，但我们的结果将这些适应性扩展到了来自典型温带栖息地的双星藻属。尽管其他附生藻类均未产生吸收UVB的化合物，但在高PAR适应后，它们在UVBR照射下均表现出更高的生长速率。这表明所评估的藻类具有针对UVBR照射的诱导防御机制，再加上它们的垫状结构，将使其适应浅水栖息地具有挑战性的光照环境。
